There should be no need for a tank to mark an order. You pull the mobs and keep hate on all of them. I do most of my roulettes on tank jobs for faster queue times. I did about 90% of the mytho grind for my animus bow tanking. It's not rocket science and there are guides out there. If a tank is losing hate because someone touched a mob he wasn't actively combo-ing on he's doing something wrong. A kill order is entirely unnecessary. It's simply a crutch for a bad tank when they use the excuse "they killed in the wrong order." Sometimes it really is the tanks fault. Sometimes it's the healer's fault. Sometimes it's the DPS fault if they can't adjust their tactics to the group. Instead of pointing fingers and blaming people, maybe everyone needs to take a step back and evaluate if there was nothing they couldn't have done better.